| Authors: |
Seong Pyo Kim, Su Hwan Kim, Jae-In Song, Zio Kim, Dongjae Shin, Yeju Park, Yujin Park, Hyung-Jin Yoon, Heung-Woo Park, Jin Youp Kim and Hyung-Jin Yoon |
| Abstract: |
Introduction: Atopic dermatitis (AD), a chronic skin disease causing inflammation and itch, is a common condition affecting approximately 20% of children worldwide. Beyond affecting physical health, AD negatively influences various aspects of daily life, including academic achievement and sleep quality. Given that recent studies have identified air pollutants as one of the major exacerbating factors of AD, elucidating the causality between air pollution and AD in children is crucial for improving young children’s quality of life. However, as randomized controlled trials for exploring it are not feasible for ethical and practical reasons, we aim to investigate the causal effects of air pollutants on AD in children using observational data.
Methods: The number of daily outpatient visits to AD in children in Seoul, the capital of South Korea, from January 2014 to December 2017, as recorded in the National Health Insurance Service database, was utilized as an outcome variable in the study. Air pollutants, such as PM (particulate matter) 2.5 and PM 10, along with nitrogen dioxide, sulfur dioxide, carbon monoxide, and ozone, were converted into air quality index (AQI) values as an exposure. Instrumental Variable (IV) analysis is a powerful quasi-experimental design for inferring causal effects in the presence of unmeasured confounding and endogeneity. It relies on a variable that is associated with the exposure but affects the outcome only through its influence on the exposure. In this study, we employed Thermal Inversion (TI)—a meteorological phenomenon in which a warm air layer becomes trapped between cooler layers above and below, resulting in temperatures increasing with altitude—as an IV, which satisfies the core assumptions of IV. Using TI as an IV, we estimated the causal effects of AQI on outpatient visits for AD in children by quantifying relative risks associated with lagged and moving average AQI exposures, utilizing a two-stage Generalized Method of Moments estimation model.
Results: A total of 1,394,739 AD outpatient visits for children between the ages of 0 and 9 years was analyzed. The effects of Inter Quartile Range (IQR) increase of AQI on AD outpatient visits for children were found to be significantly positive from lag 0 (visit date) to lag 7 (7 days before the visit date) except lag1, with the strongest effect on lag 0 (relative risk (RR):1.129, 95% confidence interval (CI):1.084-1.177, p <.0001). Furthermore, the effects of the moving averages (MA) IQR increase of AQI, spanning from MA0-1 (the average of lag0 and lag1) to MA0-7 (the average of lag0 through lag7), showed an increasing trend, becoming more pronounced over time, from MA0-1(RR:1.104, 95% CI:1.061-1.150, p <.0001) to MA0-7 (RR:1.207, 95% CI:1.150-1.267, p <.0001).
Conclusions: This study demonstrates the substantial influence of the increase of AQI on outpatient visits for AD, particularly in children. The study minimizes potential confounding factors while bolstering the hypothesis for a causal association between air quality and AD outpatient visits by using TI as an IV. Lag‐days and multiple MA windows were analyzed, and the results showed that cumulative or extended exposure to elevated AQI values may gradually raise the likelihood of AD-related medical visits of children. These findings highlight the significance of taking preemptive steps to regulate air pollution, particularly during conditions favorable to TI, from the perspective of public health. |